A Closer Look at Air Pollution in Houston: - Green Houston

Appendix 2Data Source Descriptions: NATA and AQSA national-scale assessment of air toxics for 1999 wasprepared by EPA and made public at the beginning of 2006.(U.S. EPA, 2006b) It included 176 HAPs drawn from the 188named in Section 3 of the Clean Air Amendments of 1990, andadded diesel particulate matter. The assessment included anational inventory of air toxics emissions from outdoorsources, and estimates of ambient concentrations and populationexposure.Two databases were used. First, the National EmissionInventory 1999 reported information on each pollutant in tonsreleased per year, categorized their emission source, andreported by county (U.S. EPA, 2006c). Second, theAssessment System for Population Exposure Nationwide(ASPEN) (U.S. EPA, 2006d) provided annual pollutant concentrationsmodeled by means of a computer simulation.ASPEN used estimates of air toxics emissions and meteorologicaldata from National Weather Service Stations, as wellas took into consideration other determinants such as rate,location, and height from which they are released, reactivedecay, deposition and secondary formation. The smallest geographicunit, for which the concentrations were modeled, was acensus tract, typically containing 4000 inhabitants. The tencounty area of interest comprised a total of 895 census tracts.East Houston analysis included an area of 28 census tracts.Concentrations of each pollutant were expressed in ug/m3and were presented by source of emission, such as point, area,mobile (on road and non-road), and for some pollutants asbackground. Background concentrations are based on monitoreddata, estimates from the technical literature and reportedemissions during 1999. They are attributable to unidentifiedand natural sources, previous emissions persisting in the environment,and to long-range transport. Additional information onbackground concentrations is available at:http://www.epa.gov/ttn/atw/nata1999/background.html.Extensive information on ASPEN model can be found at:http://www.epa.gov/ttn/atw/nata1999/aspen99.html.The Air Quality System (AQS) database, as compiled bythe U.S. Environmental Protection Agency (EPA), provides airmonitoring data -- ambient concentrations of criteria and hazardousair pollutants -- from monitoring sites throughout theUnited States. These concentrations are reported to the EPA byvarious agencies throughout the United States (e.g. the TexasCommission on Environmental Quality). The data can beobtained directly from the EPA in ASCII format, or can beaccessed online. The data that we obtained were in threeforms labeled as: DM_300 (exceedance data for ozone, PM 2.5and PM 10); DM_350 (raw data for HAPs, VOCs, speciated carbon,ozone, PM 2.5 and PM 10); and DM_AMP450 (annualmeans for HAPs, VOCs, speciated carbon, ozone, PM 2.5 andPM 10). Datasets were received for years 1970 through 2005.We selected 2004 as the year of analysis, since it had the mostcomplete recent data. The ten county area was used as a filterfor the data request since “COUNTY_NAME” is a variable in theAQS dataset.There were a total of 49 HAPs that were monitored andincluded in our analysis. Of those 49, 25 had cancer risk valuesand 41 had non-cancer reference values. Several VOCsthat are also defined as HAPs were duplicated in bothdatasets. This was confirmed by analysis of both the raw andsummary data.For 2004, there were 19 “species” of carbon monitoredand included in the AQS dataset for the 10 county area. Onlytwo of these were included in the final analysis as surrogatesfor diesel particulate matter, based on the recommendation ofEPA officials. Our final analysis of raw and summary data forHAPs and speciated carbons included 51 pollutants. Ozone,PM 2.5 and PM 10 were reviewed for daily exceedances for2000-2005.Pollutants are represented as “parameters” in the AQSdataset and are assigned a five digit code. Site IDs in the databaserepresent geographic locations of monitoring sites. Aparameter occurrence code (POC) is used to distinguishbetween multiple monitors at the same site that are measuringthe same parameter. So, in effect, a POC represents a monitor.Monitoring duration is also included in the data set per POC atindividual site IDs. For example, a duration code of 7 represents24 hours, whereas a duration code of 1 represents 1 hour.The particular method for collecting and analyzing samples for30